What is Fluting and How to Fix It

Fluting can be an issue on bearings if you don’t know how to look for the signs. In this post we will cover what fluting is and how to fix it when it occurs.

First, what is fluting?

Fluting is damage caused to a bearing due to an electrical current induced on the shaft of a VFD (Variable Frequency Drive) machine.

To read more about VFDs, see our previous post here.

Fluting must be addressed because it can lead to bearing wear and ultimately failure. If a bearing is experiencing fluting, the inner ring will likely have washboard-like ridges where the electrical current is wearing it down.

Bearing failure is particularly common in VFDs because the current induced upon the shaft, when the motor is not properly VFD rated, travels through the bearing as the path of least resistance to ground.

These voltages are destructive to bearings and can cause bearing failure at an exponentially faster rate.

To fix fluting

To fix fluting, the electrical current must be redirected. There are a couple ways to do this:

1. If a machine is rated at less than 100 horsepower, a carbon fiber brush may be attached to a shaft grounding ring (also called a split ring, solid ring, or a press fit) and installed on the drive side of the shaft. This will effectively redirect the current to ground and will avoid arching between the bearing components which could result in bearing failure.
2. If a machine is rated at 100 horsepower or more, a non-conductive ceramic bearing may be attached to the opposite side of the shaft in addition to the carbon fiber brush. The ceramic bearing prevents the NDE of the motor from becoming another path for current discharge to ground.

Both of these fixes effectively redirect electrical current and voltage which can cause fluting.

Knowing how to fix fluting is essential to extend the life of your bearings and to ensure your VFD machines run efficiently.

by Bertrand Wascat | | September 3, 2019
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